Filled legs in horses: how to identify the cause *H&H Plus*

Lymphangitis

Swollen or filled legs are not uncommon in horses, but are they always a cause for concern? H&H outlines the potential causes and explains when you need to seek veterinary advice...

Swollen or filled legs in horses are not uncommon during autumn and winter as horses spend more time standing in their stables. Some owners will find their horse’s legs become filled overnight, with the hind legs typically more swollen than the front. In these cases the amount of swelling is typically similar in each pair of legs (fronts or hinds).

Filled legs of this nature are caused by an abnormal accumulation of fluid in the tissues called oedema and will go down with gentle exercise or when the horse is turned out. Legs filled with oedema are typically cold, the swelling is soft and can be depressed by your finger and it is not painful to the horse. As long as there is not heat and the swelling does disappear with exercise or turnout, it’s not usually a cause for concern.

Some owners will chose to apply stable bandages to help prevent it from occuring, while others have had success using magnetic boots. Accupuncture or massage to stimulate the circulatory and lymphatic system can also help.

More serious causes of filled legs in horses

Other causes of a single filled leg include an injury or an infection, while a generalised illness, such as heart failure, may cause all four limbs to fill at once. In such cases, the filled legs will be just one part of a clearly sick horse. It will be obvious there is something wrong and that you need to call your vet.

Another critical condition affecting all four limbs is equine purpura haemorrhagica (EPH), which can follow strangles and other infections, such as equine flu. It is believed to be an allergic reaction that usually shows up two to four weeks after a strangles infection, just when you think your horse is getting better.

EPH signs vary, but can include:

Oedema of the head, limbs and other parts of the body
Fever
Depression
Tiny haemorrhages on the lips, gums and other mucous membranes, for example around the eye
Stiffness and reluctance to move
Fluid may ooze through the skin and areas of skin may die, leaving ugly raw patches

The most obvious sign that something is wrong is the oedema; even spindly legs will appear as thick as tree trunks with this condition. Aggressive treatment should be started as soon as it is suspected.

Treatment tends to involve high doses of steroids to suppress the immune response that is the underlying cause of the damage. High-dose antibiotics are also useful to control any associated infection. Practical help should include support bandages and hosing to control limb swelling, plus tempting the horse to eat and move about.

Swelling of just one leg

Far more frequently a horse will develop a localised infection involving one leg only, often following a wound. Sometimes there is an obvious area of broken skin where infection has entered; for instance, a patch of mud fever on the heels can cause the whole leg to swell. Often a tiny puncture wound is the cause and can be hard to identify. Occasionally, unidentified pus in the foot will cause swelling up the leg.

Cellulitis is the technical term for infection within the tissues. Cellulitis from a wound can result in swelling up the leg to above the knee or hock. In severe cases where the lymphatic system is also involved, this is termed lymphangitis. This means inflammation of the lymphatic system, the body’s drainage channels that carry fluid back towards the heart. When they become inflamed and blocked, fluid will accumulate.

Acute lymphangitis occurs more commonly in hindlimbs than forelimbs, and is soft tissue swelling throughout the affected limb. The superficial lymphatic vessels may appear more prominent than usual and bloodstained fluid (serum) may ooze through the taut stretched skin of the swollen areas.

The horse will be lame, in pain and often has a raised temperature. The degree of swelling inevitably results in stiffness, as the affected limb is simply too fat to bend freely, although this will often improve with gentle walking.

Your vet should be contacted as soon as this is suspected, since prompt treatment with appropriate antibiotics provides the best chance for a full recovery. The milder forms of such limb infections usually respond to treatment, unless there is a particularly unpleasant type of bacteria involved.

Severe lymphangitis can be more difficult to control. Potent intravenous antibiotics may be required in conjunction with strong anti-inflammatory treatments. Steroids are a commonly used treatment, but are a double-edged sword, since they reduce the body’s immune response as well as being anti-inflammatory. But in certain circumstances they are beneficial.

Diuretics to reduce the amount of fluid are sometimes useful and all sorts of pressure wraps have been devised to reduce the swelling. Impressive results have been achieved in some cases with intensive hydrotherapy.

Despite all efforts, it seems that once a horse has had a severe attack of lymphangitis the condition has a tendency to recur or remain as fibrous scarring, possibly because the normal fluid drainage is permanently disrupted.

In the past, many such limb infections were potentially fatal and lymphangitis can still cause major complications. It is best to catch it early and treat it aggressively.

H&H Vet Clinic: 4 May 2006

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